Invasive candidosis is difficult to diagnose and is the cause of substantial morbidity and mortality in immunosuppressed patients. The clinical symptoms are often vague and conventional blood culturing is often negative [de Repentigny L, Kuykendall R. J, Chandler F. W, Broderson J. R, Reiss E. Comparison of serum mannan, arabinitol, and mannose in experimental disseminated candidiasis. J Clin Microbiol, 1984. 19(6): p. 804-12; Gutierrez J, Maroto C, Piedrola G, Martin E, Perez J. A. Circulating Candida antigens and antibodies: useful markers of candidemia. J Clin Microbiol, 1993. 31(9): p. 2550-2; Jones, J. M., Laboratory diagnosis of invasive candidiasis. Clin Microbiol Rev, 1990. 3(1): p. 32-45]. Laboratory diagnosis of deep Candida infection is based on blood culturing, direct microscopy, and determination of Candida antigens. Anti-Candida antibodies and detection of D-arabinitol in serum or urine by gas liquid chromatography are complementary analyses [de Repentigny L, Kuykendall R. J, Chandler F. W, Broderson J. R, Reiss E. Comparison of serum mannan, arabinitol, and mannose in experimental disseminated candidiasis. J Clin Microbiol, 1984. 19(6): p. 804-12; Gutierrez J, Maroto C, Piedrola G, Martin E, Perez J. A. Circulating Candida antigens and antibodies: useful markers of candidemia. J Clin Microbiol, 1993. 31(9): p. 2550-2; Fujita, S, Hashimoto T, Detection of serum Candida antigens by enzyme-linked immunosorbent assay and a latex agglutination test with anti-Candida albicans and anti-Candida krusei antibodies. J Clin Microbiol, 1992. 30(12): p. 3132-7; Nakamura A, Ishikawa N, Suzuki H. Diagnosis of invasive candidiasis by detection of mannan antigen by using the avidin-biotin enzyme immunoassay. J Clin Microbiol, 1991. 29(11): p. 2363-7].
Antibody determination for immunodiagnosis of systemic candidosis includes latex agglutination [Dee T. H., Johnson G. M, Berger C. S. Sensitivity, specificity, and predictive value of anti-candida serum precipitin and agglutinin quantification: comparison of counterimmunoelectrophoresis and latex agglutination. J Clin Microbiol, 1981. 13(4): p. 750-3], counterimmunoelectrophoresis [Bisbe J, Miro J. M, Torres J. M, Latorre X, Alia C, Amaral M, Estivill D, Mallolas J, Trilla A, Soriano E. Diagnostic value of serum antibody and antigen detection in heroin addicts with systemic candidiasis. Rev Infect Dis, 1989. 11(2): p. 310-5; Kostiala, A. A. and I. Kostiala. Enzyme-linked immunosorbent assay (ELISA) for IgM, IgG and IgA class antibodies against Candida albicans antigens: development and comparison with other methods. Sabouraudia, 1981. 19(2): p. 123-34], indirect immunofluorescence [Quindos G, Ponton J, Cisterna R. Detection of antibodies to Candida albicans germ tube in the diagnosis of systemic candidiasis. Eur J Clin Microbiol, 1987. 6(2): p. 142-6] and enzyme-linked immunoassay [Kostiala, A. A. and I. Kostiala. Enzyme-linked immunosorbent assay (ELISA) for IgM, IgG and IgA class antibodies against Candida albicans antigens: development and comparison with other methods. Sabouraudia, 1981. 19(2): p. 123-34; Greenfield R. A., Bussey, M. J, Stephens J. L, Jones J. M. Serial enzyme-linked immunosorbent assays for antibody to Candida antigens during induction chemotherapy for acute leukemia. J Infect Dis, 1983. 148(2): p. 275-83; Navarro D, Monzonis E., Lopez-Ribot J. L, Sepulveda P, Casanova M, Nogueira J. M, Martinez J. P. Diagnosis of systemic candidiasis by enzyme immunoassay detection of specific antibodies to mycelial phase cell wall and cytoplasmic candidal antigens. Eur J Clin Microbiol Infect Dis, 1993. 12(11): p. 839-46]. The antibody tests often express a low sensitivity, i.e. in most cases they fail to discriminate between disseminated and superficial candidosis [Martinez J. P, Gil M. L, Lopez-Ribot J. L., Chaffin W. L. Serologic response to cell wall mannoproteins and proteins of Candida albicans. Clin Microbiol Rev, 1998. 11(1): p. 121-41]. In order to increase the specificity of the immunodiagnostic tests, various forms of antigens from C. albicans including cytoplasmic extract and cell wall antigens [Sendid, B, Tabouret M., Poirot J. L, Mathieu D, Fruit J, Poulain D. New enzyme immunoassays for sensitive detection of circulating Candida albicans mannan and anti-mannan antibodies: useful combined test for diagnosis of systemic candidiasis. J Clin Microbiol, 1999. 37(5): p. 1510-7; Zoller L, Kramer I, Kappe R, Sonntag H. G. Enzyme immunoassays for invasive Candida infections: reactivity of somatic antigens of Candida albicans. J Clin Microbiol, 1991. 29(9): p. 1860-7] have been used.
The cell wall of C. albicans makes up approximately 30% of the total weight of the cell and is composed of carbohydrate (glucan, mannan, and chitin), small amounts of protein, and lipids. The outermost layer of the cell wall is composed of mannoprotein while the deeper layer is made up of β-glucan and chitin microfibrils [Reiss E., Hearn V. M, Poulain D, Shepherd M. G. Structure and function of the fungal cell wall. J Med Vet Mycol, 1992. 30(Suppl 1): p. 143-56]. Mannoprotein is a complex glycoprotein composed of mannose polymers and oligomers attached in various ways to a peptide. Mannose or unbranched mannose oligomers are also attached directly to a peptide via the hydroxyl groups of serine or threonine residues [Nelson R. D, Shibata N, Podzorski R. P, Herron M. J. Candida mannan: chemistry, suppression of cell-mediated immunity, and possible mechanisms of action. Clin Microbiol Rev, 1991. 4(1): p. 1-19].
Anti-mannan antibodies appear to be one of the major anti-Candida antibodies in human sera [Jones J. M. Quantitation of antibody against cell wall mannan and a major cytoplasmic antigen of Candida in rabbits, mice, and humans. Infect Immun, 1980. 30(1): p. 78-89]. The glucan polymers which are in greater abundance than mannan in the C. albicans cell wall are immunologically less active [Nelson R. D, Shibata N, Podzorski R. P, Herron M. J. Candida mannan: chemistry, suppression of cell-mediated immunity, and possible mechanisms of action. Clin Microbiol Rev, 1991. 4(1): p. 1-19]. Since mannan is a major antigenic component of the cell wall, different chemical and enzymatic methods have been used to extract mannan from C. albicans, but these methods have limitations. When mannan is extracted by hot alkali treatment, mannose-serine, and mannose-threonine linkages, phosphodiester linkages and some peptide bonds are cleaved at basic pH. The loss of the O-linked oligosaccharides attached via phosphate groups leaves a modified mannan product that is greatly altered in its antigenicity and biological effects [Nelson R. D, Shibata N, Podzorski R. P, Herron M. J. Candida mannan: chemistry, suppression of cell-mediated immunity, and possible mechanisms of action. Clin Microbiol Rev, 1991. 4(1): p. 1-19]. Hot water extraction may denature the protein structure in mannoproteins. Thus the extraction procedures may modify the mannan product and alter the antigenicity.
Antibody tests have been less useful mainly because anti-Candida antibodies are often present in healthy individuals which is considered to be a consequence of immunization from Candida in the commensal flora (Odds, F. C., and E. G. Evans. 1980. Distribution of pathogenic yeasts and humoral antibodies to candida among hospital inpatients. J Clin Pathol 33:750-6). Furthermore, the antibody response of Candida-infected patients is often impaired by the underlying condition, particularly in non-surgical patients.
The human IgG subclasses differ with respect to physical, chemical, and biological properties. IgG1, IgG2, and IgG3 activate complement, although IgG2 less efficiently. In contrast to IgG1, IgG3, and IgG4, IgG2 demonstrates no or low binding capacity to human mononuclear cells and neutrophils. The subclass distribution of the antibody response is influenced by the nature of the immunogen, the localization of the entry into the body, and age of the host. IgG1 and IgG3 antibodies are mainly induced by protein antigens whereas IgG2 is predominating against polysaccharides (Hammarstrom, L., M. Granstrom, V. Oxelius, M. A. Persson, and C. I. Smith. 1984. IgG subclass distribution of antibodies against S. aureus teichoic acid and alpha-toxin in normal and immunodeficient donors. Clin Exp Immunol 55:593-601; Mattsby-Baltzer, I., L. Edebo, B. Jarvholm, B. Lavenius, and T. Soderstrom. 1990. Subclass distribution of IgG and IgA antibody response to Pseudomonas pseudoalcaligenes in humans exposed to infected metal-working fluid. J Allergy Clin Immunol 86:231-8; Shakib, F., and D. R. Stanworth. 1980. Human IgG subclasses in health and disease. (A review). Part I. Ric Clin Lab 10:463-79).